Balloon power isn't just a load of hot air

For those who dislike the sight of wind turbines on the horizon, would a spectacular hot-air balloon farm be more acceptable?

Ian Edmonds, an environmental consultant with Solartran in Brisbane, Australia, has designed a giant engine with a balloon as its "piston". A greenhouse traps solar energy, providing hot air to fill the balloon. As the balloon rises, it pulls a tether, which turns a generator on the ground. Once the balloon has reached 3 kilometres, air is released through its vent and it loses buoyancy. This means less energy is needed to pull the balloon back down again, resulting in a net power gain (Renewable Energy, DOI: 10.1016/j.renene.2008.06.022). "It is like a huge two-stroke engine, with a capacity of 45 million litres, a stroke of 3 kilometres, and a frequency of one revolution per hour," says Edmonds.

For roughly the same cost as ...

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